Identifying Sources of Long-Distance Transported Pollution to the Arctic using δ13C in CH4 and Particle Dispersion Modelling.

A stratified pollution plume of increased CH4 was identified at ~2000ft to ~7000ft altitude between the North coast of Norway and Svalbard on 21st July, 2012. The increased CH4 was identified through continuous CH4 measurements using a fast greenhouse gas analyser on board the NERC FAAM aircraft as part of the MAMM (Methane in the Arctic: Measurements and Modelling) campaign. Measurements of δ13C in CH4 on air samples taken whilst the aircraft was in the pollution plume demonstrate that the plume has a δ13C in CH4 source signature of 70 ‰. (±2.1 ‰). A δ13C source signature of 70 ‰ (±2.1 ‰) is within the expected boundaries of δ13C for wetland emissions in the Arctic (-70 to -60‰ (Dlugokencky, Nisbet, Fisher, & Lowry, 2011)). The NAME (Numerical Atmospheric-dispersion Modelling Environment) model was run backwards from the measurement locations to identify periods where the measured air mass was in contact with the surface (lowest 300 m of the atmosphere). Combining the results together show that the likely source of the elevated methane measured is from wetlands located in North-West Russia. By sampling stratified air at altitude using the FAAM aircraft as a measurement platform, the joint application of isotopic source identification and NAME modelling allows identification of methane plumes from sources that we would otherwise not be able to sample, due to either remote access and / or political reasons (providing that suitable meteorological conditions exist). The use of this joined up approach will give us an extra tool in adding data to the global inventory of δ13C in CH4 source signatures and will enable better understanding of the sources of above background concentrations of CH4 to the Arctic.